ISO 15788-1:1999

Overview

ISO 15788-1:1999 specifies a reference analytical method for the determination of stigmastadienes in vegetable oils using capillary-column gas chromatography (GC). Stigmastadienes (mainly 3,5‑stigmastadiene plus a minor 2,4‑isomer) are steroidal hydrocarbons formed during high‑temperature refining. This method is particularly aimed at detecting low concentrations in virgin oils (e.g., virgin olive oil) and is suited to identifying the presence of refined vegetable oils in cold‑extracted virgin products.

Key topics and technical requirements

• Scope and applicability: Applicable to all vegetable oils but reliable for stigmastadiene contents between approximately 0.01 mg/kg and 4.0 mg/kg; limit of detection cited as 0.01 mg/kg.
• Analytical principle: Isolation of the unsaponifiable fraction, silica‑gel column chromatography to isolate the steroidal hydrocarbon fraction, followed by analysis by capillary‑column GC with flame ionization detection (FID).
• Internal standard: Use of 3,5‑cholestadiene as an internal standard for quantification; response factor assumed to be 1.
• Reagents and preparation: Hexane (distilled), alcoholic KOH saponification, silica gel 60 for column fractionation, and reference solutions including 3,5‑stigmastadiene and n‑nonacosane for system checks.
• GC conditions (typical): Fused‑silica capillary column (5% phenylmethylsilicone), injector ≈300 °C, detector ≈320 °C, split injection (1:5), oven program starting ~235 °C with ramp to ~285 °C; carrier gas helium or hydrogen.
• Quality control & precision: Method includes chromatographic checks, fraction volume optimization to separate saturated vs steroidal hydrocarbons, storage recommendations (keep residues in solvent, refrigerated), and interlaboratory precision data summarized from collaborative studies.

Applications

• Olive oil authenticity testing - detect adulteration of virgin olive oil with refined oils.
• Quality control in refining - monitor formation of thermal degradation products during bleaching/deodorization.
• Regulatory and labeling compliance - support identity criteria for virgin oils and verify processing claims.
• Research and method validation - reference method for comparison with alternative techniques.

Who uses this standard

• Food and oil testing laboratories
• Olive oil producers and refiners
• Food safety and regulatory authorities
• Research organizations studying oil processing and authenticity

Related standards

• ISO 15788-2 - companion method using high‑performance liquid chromatography (HPLC).
• Reference to ISO 5725 for statistical treatment of precision data (interlaboratory study).

Keywords: ISO 15788-1, stigmastadienes, vegetable oils, capillary-column gas chromatography, olive oil authenticity, unsaponifiable fraction, 3,5-cholestadiene, FID, refined oil detection.